Palladium plating by chemical reduction



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PALLADIUM PLATING BY CHEMICAL REDUCTIGN Richard N. Rhoda, Westfield, N.J., and Ann-Mari Madison, Bellevue, Wash., assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware i 1 No Drawing. Application March 3, 1958 Serial N0. 718,455

21 Claims. c1. 106-1) The present invention relates to the deposition of electrochemical It has now beendiscovered that continuous, smooth, adherent plates of palladium may bechemically deposited by means of a special bath.

It is an object of the present invention to provide an Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates the production of smoothadherent deposits of palladium on objects having a catalytic metal surface by catalyzed chemical deposition from Water-containing plating baths. The baths contemplated in accordance with the present a concentration of at least greater than 2 m.p.l. and up In practice, the aforemenv bl 2,915,406 Patented Dec. 1, 1959 2 tioned bath is maintained at a temperature between about 30 C. to about C. having a surface layer of, a substance which catalyzes the reduction of divalent palladium by hydrazine is introduced into the bath, palladium is reduced at or near the ladium, platinum, ruthenium, silver, steel, tin, tungsten Alloys rich in nickel and cobalt include austenitic nickel-chromium alloys, in-

cluding nickel-chromium-iron and nickel-chromium-cobalt and cobalt-chromium alloys, including cobalt-chromium-- um and boron which may optionally be present in the alloys. Such alloys include the nickel-chromium-cobalt alloys and nickel-chromium alloys which are sold commercially under the trademarks of Inconel 700 and Inconel X.

the reduction of palladium in accordance with the invention are generally metals which tacked by the bath. It is to be noted, however, that sub,-

he term stabilizing agent as used herein, refers to clude the di-sod1um salt of ethylen -diaminetetraacetic acid (EDTA), aliphatic ketones containing from 3 up to about 5 carbon atoms per molecule and dihydroxy-,

dialkyl sulfides having up toS carbon atoms per molecule. 3-pentanone, di- [Z-hydroxyethyl] sulfide otherwise known as 2,2-thiodiethanol (HOC H S-C H OH), acetone f ammonium salts of mono-basic and di-basic mineral acids such as ammonium chloride, ammonium nitrate and ammonium sulfate have thus, are also inen an object made of, or

noethyl ethanol-amine otherwise known as N-(Z hydroxyethyl) ethylene diamine, (NH CH CH NHCH CH OH), may be present in the bath only in a concentration up to about 9 moles per liter.

In carrying the invention into practice, it is advan tageous to maintain the bath composition within the following range of composition:

Constituent: Moles/liter Divalent palladium 0.03-0.20 NH or amine 7-10 Hydrazine 0005-001 Stabilizing agent 0.01-0.10 Water Balance 2 The pH of these baths lies between about 9 and 11 and the baths are advantageously maintained at a temperature of about 30 C. to about 70 C. during deposition. Divalent palladium may be introduced intothe bath as the chloride, the chloropalladite and the amminochloride. A typical bath contains about 3.2 to about 21.2 g.p.l. of divalent palladium (about 0.03 to about 0.2 m.p.l.), about 245 to about 350 g.p.l. of ammonium hydroxide (about 7 to about m.p.l.), about 0.16 to about 0.32 g.p.l. of hydrazine (about 0.005 to about 0.01 m.p.l.), about 3.36 to about 33.6 g.p.l. of the disodium salt of EDTA (about 0.01 to about 0.1 m.p.l.) and the balance being essentially water. It is preferred to maintain the bath at a temperature of about 30 C. to about 70 C. and the pH range should be about 9 to 11. It is to be observed that the reduction of divalent palladium by hydrazine is catalyzed by a large number of substances. Accordingly, since it is undesirable that the reduction take place in any location other than on the catalytic surface, the bath should be free of suspended solid particles. Advantageously, before it is used for plating, the bath is filtered through a fine filter in order to eliminate centers or nuclei of reduction. A filter made of a fine grade of fritted glass is preferred over a filter made of organic material, since organic material may tend to reduce palladium and thus provide possible centers for continuing reduction.

When it is desired to deposit palladium on the surface of a metal object, for example, an object made of a metal which catalyzes the reduction of divalent palladium by hydrazine, a bathwithin the composition limits set forth hereinbefore is preferred. Advantageously, the bath is made up by the addition of two stock reagents, the first being an aqueous solution containing dissolved palladium, ammonium hydroxide and the di-sodium salt of EDTA and the second being an aqueous solution coni taining hydrazine as hydrazine sulfate, N H .H SO or hydrazine hydrate, N H .H O. Hydrazine may also be added in the form of a commercially available aqueous solution. The palladium in the first solution is in the form of tetramminepalladium (II) chloride This complex palladium salt is prepared by adding concentrated ammonium hydroxide to an aqueous solution of palladous chloride. A precipitate of diamminepalladium (II) chloride (Pd(NH Cl is formed thereby. Upon further addition of ammonium hydroxide this precipitate is redissolved forming, with an excess of ammonium hydroxide, a substantially colorless solution containing the aforementioned tetramminepalladium (II) chloride. Preferably, the hydrazine stock solution is added to the palladium containing stock solution immediately before the plating operation is to begin. The object to be plated is thoroughly cleansed, taking care that the surface is free from such material as lubricating oils, etc., which would interfere with the chemical reduction. These interfering materials are for the most part identical to .those materials which cause imperfectionsinelectrodeposits and are well known to those skilled in the art of electroplating. After the j t h been thoroughly cleaned, it is rinsed in distilled water and immersed in the aforementioned palladium chemical plating bath. The initiation of chemical plating of palladium is indicated by the appearance of a multiplicity of small bubbles on the surface of the object. The object is kept in the bath until a sufficient thickness of palladium is obtained thereon, or until there is no further indication of plating on the surface of the object due to depletion of the bath. If deposition ceases and the bath still contains dissolved palladium, plating may again be initiated, usually by the introduction of additional hydrazine solution. This addition should be made after the bath has been cooled to about 10 C. An additional filtration of the bath at this stage is often advisable. If a black precipitate appears in the bath, the object should be removed and the use of the bath discontinued. When decomposition of the bath, as indicated by the aforementioned black precipitate, takes place, the precipitate consisting of finely divided palladium, may be allowed to settle and the supernatant liquid may be decanted. The finely divided palladium may then be recovered and can be redissolved by processes well known to those skilled in the art, for example, by subjecting the material to the action of aqua regia. In operating the bath as described hereinbefore, care should be taken that substances such as iodide ion, stannous ionand other divalent palladium precipitants (e.g., dimethylglyoxime, cyanides, thionalide, pyridine and hydroxyquinolines), should be absent from the bath. Neither metallic zinc nor magnesium should be introduced into or brought in contact with the bath since they cause the precipitation of the palladium ion as spongy palladium metal.

When operating the aforementioned baths, it is to be noted that the rate of deposition of palladium is dependent upon a number of variables. With increasing content of dissolved palladium, all other factors being equal, the rate of deposition increases. The rate of deposition, however, depends upon the nature of the complexing agent and the specific amine used. The rate of deposition likewise increases as the ratio of hydrazine to divalent palladium increases. As the temperature increases, the rate of deposition also increases. All other factors being equal the rate of agitation will also affect the A particular advantage of the baths of the present invention is afforded by the fact that all surfaces of objects which are exposed to the bath may be coated with palladium through the use thereof. The agitation of the bath by the evolution of gas at the catalytic surface of the object tends to minimize the depletion of the bath at or near interior surfaces such as in blind depressions.

For the purpose of giving those skilled in the art a better understanding of the invention and/ or a, better appreciation of the advantages of the invention the following illustrative examples are given:

Example I A bath containing 4.3 g.p.l. of divalent palladium, 0.29 g.p.l. of hydrazine, 33.6 g.p.l. ofthe di-sodiurn salt of EDTA, 350 g.p.l. of ammonium hydroxide and the balance essentially water was provided. The pH of the bath was 10.5. A platinum wire to be plated having the dimensions of 0.04 inch diameter and 2 inches long was inserted in this bath while thebath was maintained at a temperature of C. After a few minutes, the wire increased in weight by 0.0076 gram, indicating the deposition of a palladium plate 0.00015 inch thick. The plate was smooth, bright and adherent and had a Knoop hardness number of 257 K.H.N.

Example II A bath containing 0.04 m.p.l. of divalent palladium, 7 m.p.l. of aminoethyl ethanolamine, 0.0075 m.p.l. of hydrazine, 0.05 m.p.l. of the disodium salt of EDTA, with the balance water, was provided. The bath had a pH in excess of 12.5 and was maintained at a temperatnre of about 60 C. A nickel wire 0.040 inch in diameter and 2 inches long was inserted in the bath. gray deposit of on the nickel wir Example III A bath containing 0.20 m.p.l. of divalent palladium, 7 m.p.l. of

Example IV A bath containing 0.06 m.p.l. of

Example V An aqueous palladium plating bath containing 0.03 m.p.l. of divalent palladium, 8 m.p.l. of ammonia, 0.0075

Example VI A palladium plating bath containing 0.04 m.p.l. of divalent palladium, 9 m.p.l. of ethylamine, 0.0075 m. .l. of hydrazine, 0.05 m.p.l. of. the disodium salt of with the balance water, was provided.

After 10 minutes, an adherent, gray, ductile deposit of palladium was obtained.

Example VII A palladium plating bath containing 0.1 m.p.l. of divalent palladium, 7 m.p.l. of ammonia, 0.01 m.p.l. of hydrazine, 0.05 m.p.l. of 2-2'-thiodiethanol, with the balance water was established.

3.5 milligrams and was 0.07 mil thick.

Example VIII An aqueous palladium plating bath containing 0.04 m.p.l. of divalent palladium, 8 m.p.l. of ammonia, 0.010 m.p.l. of hydrazine, 0.05 m.p.l. of 3-pentanone, with the balance water, Was provided. The bath had a pH of Example IX A palladium plating bath containing 0.16 m.p.l. of divalent palladium, 9 mp1 of ammonia, 00075 m l of the deposit was 224 deposit Weighed 14.8 mil Example X An aqueous ammoniacal plating bath containing 0.04 m.p.l. of div wire used in Example 11 was inserted about one-half hour a bright, ductile,

other parts in electron tubes.

The present invention is also applicable to the production of electrical contacts and connectors, electrical components for glass-to-metal seals and diffusion barriers, protective coatings, corrosion protection and tarnish protection.

Although the We claim: 1. A bath for depositing phase, Water-containing liquid having in solution about moles per liter.

3. A bath for depositing palladium comprising a single.- phase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 up to about-0.10 mole per liter of astabilizing agent selected from the group. consisting-of aliphaticacid and 2,2'-thiodiethanol, about 7 up toabout 10 moles per liter of ammonia and the balance esse tiallywater;w

said water being in a concentration of at least 2 ml'es per liter. I

4. A bath for depositing palladium comprisinga singlephase, water-containing liquid having in solution about 0.001 to about 0.25 mole per liter of divalent palladium, about 0.002 up to about 0.05 mole per liter of hydrazine, about 0.005 up to about 0.25 mole per liter of a stabilizing agent selected from the group consisting of aliphatic ketones containing from 3 to about 5 carbon atoms per molecule, ammonium salts of mono and di-ba'sic mineral acids, the disodium salt of ethylenediaminetetraacetic acid, and 2,2'- hiodiethanol, about 2.5 up to about 14 moles per liter of ethylamine and the balance essentially water.

5. A bath for depositing palladium comprising a singlephase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 up to about 0.10 mole per liter of a stabilizing agent selected from the group consisting of aliphatic ketones containing from 3 to about 5 carbon atoms per molecule, ammonium salts of mono and di-basic mineral acids, the disodium salt of ethylenediaminetetraacetic acid and 2,2-thiodiethanol, about 7 up to about 10 moles per liter of ethylamine and the balance essentially water.

6. A bath for depositing palladium comprising a singlephase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 up to about 0.10 mole per liter-of a stabilizing agent selected from the group consisting of aliphatic ketones containing from 3 to about 5 carbon atoms per molecule, ammonium salts of mono and di-basic mineral acids, the disodium salt of ethylenediaminetetraacetic acid and 2,2-thiodiethanol, about 7 up to about 9 moles per liter of aminoethyl ethanolamine and the balance essentially water, said water being in a concentration of at least 2 moles per liter.

7. A bath for depositing palladium comprising a singlephase, water-containing liquid having in solution about 0.001 to about 0.25 mole per liter of divalent palladium, about 0.002 up to about 0.05 mole per liter of hydrazine, about 0.005 to about 0.25 mole per liter of the disodium salt of ethylenediaminetetraacetic acid, about 2.5 up to about 14 moles per liter of at least one substance selected from the group consisting of ammonia and aliphatic organic compounds containing a primary amine group and having up to 5 carbon atoms per molecule and the balance essentially water, said water being in a concentration of at least 2 moles per liter.

8. A bath for depositing palladium comprising a singlephase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 up to about 0.10 mole per liter of the disodium salt of ethylenediaminetetraacetic acid, about 7 up to about 10 moles per liter of at least one substance selected from the group consisting of ammonia and aliphatic organic compounds containing a primary amine .group and having up to 5 carbon atoms per molecule and the balance essentially water, said water being in a concentration of at least 2 moles per liter.

9. A bath for depositing palladium comprising a singlephase, water-containing liquid havingin solution about 0.03 to about 0.20 mole per liter of divalent palladium, abo'ut'0.005 up to about 0.01 mole per liter of hydrazine,

about 0.01 to about 0.10 mole per liter of the disodium about 10 moles per liter'of ammonia and the balance essentially water, said water being in a concentration of at least 2 moles per liter;

10. A bath for depositing palladium comprising a single-phase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0005 up to about 0.01 mole per liter of hydrazine, about 0.01 to about 0.10 mole per liter of the disodium salt of ethylenediaminetetraacetic acid, about 7 up to about 10 moles per liter of ethylamine and the balance essentially water, said water being in a concentration of at least 2 moles per liter.

11. A bath for depositing palladium comprising a single-phase, water-containing liquidhaving in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 to about 0.10 mole per liter of the disodium salt of ethylenediaminetetraacetic acid, about 7 up to about 9 moles per liter of aminoethyl ethanolamine and the balance essentially water, said water being in a concentration of at least 2 moles per liter.

12. A bath for depositing palladium comprising a single-phase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 to about 0.10 mole per liter of 3-pentanone, about 7 up to about 10 moles per liter of ammonia and the balance essentially water.

13. A bath for depositing palladium comprising. a single-phase, water-containing liquid having in solution about 0.03 to about 0.20 mole per liter of divalent palladium, about 0.005 up to about 0.01 mole per liter of hydrazine, about 0.01 to about 0.10 mole-per liter of 2,2' thiodiethanol, about 7 up to about 10 moles per liter of ammonia and the balance essentially Water.

14. An auto-catalytic process for the production of adherent deposits of palladium on objects which comprises providing an object having at least a surface layer of catalytic metal and immersing said'object'ina singlephase liquid bath having a' pH from about 9 to about 11 and containing from about 0.03 to about 0.20 mole per liter of divalent palladium, about 7 up to about 10 moles per liter of a substance selected from the group consisting of ammonia and aliphatic primary amines containing up to about 5 carbon atoms per molecule,,about 0.01 to about 0.10 mole per liter of astabilizing agent selected from the group consisting of aliphatic ketones containing from 3 to about 5 carbon atomsv per molecule, ammonium salts of mono and di-basic. mineral acids, the disodium salt of ethylenediaminetetraacetic acid and 2,2'thiodiethanol, fromabout 0.005 tov about 0.01 mole per liter of hydrazine with the'balance at least 2 moles per liter essentially Water while maintaining said bath at a temperature between about 30 C. to about C.

15. An auto-catalytic process for the production of adherent deposits of palladium on objects which comprises providing an object having at least a surface layer of catalytic metal and immersing said object in a singlephase liquid bath having a pH from about 9 to about 11 and containing from about 0.03 to about 0.20 mole per liter of divalent palladium,- about 7 up to about 10 moles per liter of a substance selected from the group consisting of ammonia and aliphatic primary amines containing up to about 5 carbon atoms per molecule, about 0.01 to about 0.10 mole per liter of a stabilizing agent selected from the group consisting of aliphatic ketones containing from 3 to about 5 carbon atoms per molecule, ammonium salts of mono and di-basic mineral acids, the disodium salt of ethylenediaminetetraacetic acid and 2,2'-thiodiethanol, from about 0.005 to about 0.01 mole per liter of hydrazine with the balance at least 2 moles. per liter essentially water while maintaining said bath at a temperature between about 30 C. to about to about 10 moles per liter of at least one substanct 70 C. selected from the group consisting of ammonia and ali 16. An auto-catalytic process for the production of phatic organic compounds containing a primary amine adherent deposits of palladium on objects which comgroup and having up to carbon atoms per molecule prises providing an object having at least a surface layer 5 and the balance essentially water, said water being in a of catalytic metal and immersing said object in a singleconcentration of at least 2 moles per lite phase liquid bath containing from about 0.001 to about 20. An auto-catalytic process for the production of 0.25 mole per liter of divalent palladium, about 2.5 up adherent deposits of palladium on objects which comto about 14 moles per iter of a substance selected from prises providing an ob ect having at least a surface layer the group consisting of ammonia and aliphatic primary of catalytic metal and immersing said object in a singleamines containing up to about 5 carbon atoms per molphase liquid bath having a pH Irom about 9 to about 11 ecule, about 0005 to about 025 mole per liter of a and containing from about 003 to about 020 mole per stabilizing agent selected from the group consisting of liter of divalent palladium about 7 up to about 10 aliphatic ketones containing from a to about 5 carbon moles per liter of a substance selected from the group atoms per molecule, ammonium salts of mono and di- 15 consisting of ammonia and aliphatic primary amines conbasic mineral acids, the disodium salt of ethylenedraminetaining up to about 5 carbon atoms per molecule, about tetraacetic acid and 2,2-thiodiethanol, from about 0.002 0.01 to about 0.10 mole per l1ter or the disodium salt to about 0.05 mole per liter of hydrazine With the balance of ethylenediaminetetraacetic acid, from about 0.005 to at least 2 moles per liter essentially Water While mainabout 0.01 mole per liter of hydrazine with the balance taining said bath at a temperature between about 30 C. 0 at least 2 moles per liter essentially Water while mainto about 80 C. taining said bath at a temperature between about 30 C.

17. A bath for depositing palladium comprising a to about 80 C. singlephase, Water-containing liquid having in solution 21. An auto-catalytic process for the production of about 0.03 to about 0.2 mole per liter of divalent paladherent deposits of palladium on objects Which comladium, about 0.005 up to about 0.01 mole per liter of prises providing an object having at least a surface layer hydrazine, about 0 01 up to about 0 10 mole per liter of of catalytic metal and immersing said object in a single- S-pentanone, about 7 up to about 10 moles per liter of phase llqllld bath having a pH from about 9 to about at least one substance selected from the group consist- 11 and containlng from about 0 03 to about 020 mole mg of ammonia and aliphatic organic compounds conper liter of divalent palladium, about 7 up to about 10 taining a primary amine group and having up to 5 carmoles per liter of ammonia, about 0.01 to about 0.10 bon atoms per molecule and the balance essentially Water, mole per liter of a stabilizing agent selected from the sard Water being in a concentration of at least 2 moles group consisting of aliphatic ketones containing from 3 per liter. to about 5 carbon atoms per molecule, ammonium salts 18. A bath for depositing palladium comprising a of mono and di-basic mineral acids, the disodium salt single-phase, water-containing liquid having in solution of ethylenediaminetetraacetic acid and 2,2'-thiodiethanol, about 0.03 to about 0.2 mole per liter of divalent palfrom about 0.005 to about 0.01 mole per liter of hydraladium, about 0.005 up to about 0.01 mole per liter of zine with the balance at least 2 moles per liter essentially hydrazine, about 001 up to about 0.10 mole per liter Water while maintaining said bath at a temperature liter of at least one substance selected from the group 40 consisting of ammonia and aliphatic organic compounds References Cit d in the fil of this patent containing a primary amine group and having up to 5 carbon atoms per molecule and the balance essentially UNITED STATES PATENTS water, said water being in a concentration of at least 2 2,186,452 Freund et al. Jan. 9, 1940 moles per liter. 2,560,979 Pessel July 17, 1951 19. A bath for depositing palladium comprising a 2,602,757 Kantrowitz et al. July 3, 1952 single-phase, water-containing liquid having in solution 2,690,402 Crehen Sept. 28, 1954 about 0.03 to about 0.20 mole per liter of divalent pal- 2,702,253 Bergstrom Feb. 15, 1955 ladium, about 0.005 up to about 0.01 mole per liter of 2,776,918 Bersworth Jan. 8, 1957 hydrazine, about 0.01 up to about 0.10 mole per liter of 2,819,187 Gutzeit et al. Jan. 7, 1958 ammonium salts of di-basic mineral acids, about 7 up 

1. A BATH FOR DEPOSITING PALLADIUM COMPRISING A SINGLE PHASE, WATER-CONTAINING LIQUID HAVING IN SOULATION ABOUT 0.001 TO ABOUT 0.25 MOLE PER LITER OR DIVALENT PALLADIUM, ABOUT 0.002 UP TO ABOUT 0.05 MOLE PER LITER OF HYDRAZINE, ABOUT 0.005 UP TO ABOUT 0.25 MOLE PER LITER OF A STABILIZING AGENT SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC KETONES CONTAINING FROM 3 TO ABOUT 5 CARBON ATOMS PER MOLECULE, AMMONIUM SALTS OF MONO AND DI-BASIC MINERAL ACIDS, THE DISODIUM SALT OF ETHYLENEDIAMINETERAACETIC ACID AND 2,2''-THIODIETHANOL, ABOUT 2.5 UP TO ABOUT 14 MOLES PER LITER OF AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF AMMONIA AND ALIPHATIC ORGANIC COMPOUND CONTAINING A PRIMARY AMINE GROUP AND HAVING UP TO 5 CARBON ATOMS PER MOLECULE AND THE BALANCE ESSENTIALLY WATER, SAID WATER BEING IN A CONCENTRATION OF AT LEAST 2 MOLES PER LITER. 